Code-Bin #680 - Circular Primes

Circular Primes
Posted by: amenon | June 9, 2010 @ 5:31am

Ruby Code

$primes = []

def read_primes_from_file file_loc
  primes_unparsed = File.new(file_loc, "r")
  primes_up_str = primes_unparsed.gets
  primes_as_strs = primes_up_str[1...-2].split(" ")
  $primes = primes_as_strs.collect { |prime| prime.to_i }
  primes_as_strs = nil
  primes_up_str = nil
  primes_unparsed.close
  primes_unparsed = nil
end

def is_prime n
  return false if (0..1).include? n
  $primes.each { |prime| return false if n%prime == 0}
  true
end

def prime_check n
  ('1' * n) !~ /^1?$|^(11+?)\1+$/
end

def find_from_to first, last
  (first..last).each { |num| $primes << num if is_prime num }
end

def is_circular_prime n
  num_str = n.to_s
  str_len = num_str.length
  
  (0...str_len).each {|i| 
    return false unless prime_check(num_str.to_i)
    num_str = num_str[1..-1] + num_str[0...1]
  }
  true
end
p "Reading Primes From File"
read_primes_from_file "primes.db"
p "Read successfully. Last Prime: #{ $primes[0] }"

p "Checking for Circular Primes"
count_of_circ_primes = $primes.inject(0) { |count, prime|
  if is_circular_prime(prime)
    count += 1
    print "."
  else
    count
  end
}

p count_of_circ_primes

Syntax Highlighting

[Open in new window]

Author Comments

none

Rating

4.41 / 8
39 Votes